1. Field of the Invention
The present invention concerns a method and a device to palletize packages by means of a manipulator, in particular a robot.
2. Description of the Prior Art
For example, it is known from DE 10 2007 001 263 A1 to stack individual goods or goods containers (which are uniformly designated as “packages” in the following) into package stacks by means of an automatic palletizing machine or robot, i.e. to palletize them. For this the positions of the individual packages in the package stack must be predetermined in a palletizing or loading pattern.
To generate such a palletizing pattern, offline algorithms are known on the one hand in which the palletizing pattern is predetermined in advance on the basis of all packages to be palletized. Package stacks can thus be advantageously optimized with regard to one or more quality criteria and boundary conditions and, for example, densely packed and stable stacks can be generated and relations between packages (for example a parallel arrangement of packages of the same good type) can be taken into account.
A sequence of gripping or approach positions in which the manipulator must take up the packages then results from the globally optimal palletizing pattern of such a type. If the packages are, for example, individually delivered on a continuous transporter, this series of grip positions determines the order in which the packages must be delivered. If this order is disrupted, the preplanned palletizing pattern cannot be executed.
For this purpose, it is known to then manually handle packages, for example to correct the order of the delivered packages by insertion, removal or exchange of packages, or to finish the palletizing by hand. Like any manual intervention in automated processes, this reduces the reliability and the achievable operating and cycle times, requires extensive safety measures to protect the personnel in interaction with manipulators, and is not possible for some packages due to the weight of the packages or the dimensions of packages, stacks or palletizing station.
Another known solution is to always maintain multiple packages—for example by buffering delivered packages in a sorter, for example a ring buffer, or providing different homogenous package reserves (stores)—so that it is ensured that a package provided to be accepted with the manipulation is always made available in a predetermined grip position. However, given a large number of different packages, neither are effective nor can be realized without significant cost in storage space.
From EP 1 211 203 B1, an online method is known in which the palletizing pattern is provided directly on the basis of packages actually provided in grip positions. For this a position in the previously generated sub-stack is calculated for every package from a buffer. A disadvantage of this approach is that only a locally optimized palletizing pattern is generated, such that the entire stack is normally worse with regard to packing density, stability or other quality criteria and boundary conditions relative to a stack planned in advance under consideration of all packages to be palletized.